This invention relates generally to current limiting fuses and specifically to general purpose current limiting fuses having localized regions of evolved gas for arc-quenching and suppressing.
Current limiting fuses of the type which utilize the voltage of the fuse arc for current limitation are known. It is also known to provide pulverulent arc quenching material or sand to absorb the energy of a burning or fusing fuse element during the fusing process so that the fuse will not explode during the fusing operation. It is also known to provide mandrels or cores of gas evolving material to evolve an arc quenching gas during the fusing operation. The sand tends to confine the arc radially and thus sustain its current limiting voltage in addition to absorbing the energy of the arc. However, the evolved gas exerts pressure against the inside of the fuse housing and ferrules which may lead to rupture of the fuse housing or blow off of the ferrules. It is also known that the amount of evolved gas may be reduced by providing certain types of mandrels or support beams which evolve gas locally in controlled small quantities so that the pressure within the fuse housing does not increase significantly even through the positive effects of the presence of arc suppressing gas are generally maintained. Fuses of this type are described in the previously mentioned copending application Ser. No. 483,602 and in U.S. Pat. No. 3,437,971, entitled "Current Limiting Fuse", issued to H. W. Mikulecky on Apr. 8, 1969 and U.S. Pat. No. 3,569,891, entitled "Current Limiting Fuse" issued to F. L. Cameron on Mar. 9, 1971 and assigned to the same assignee as the present application. The previously mentioned application Ser. No. 483,602 represents an advance in the state of the art inasmuch as the production of arc quenching gas is significantly reduced even though the benefits of the presence of the arc quenching gas are not significantly reduced. Other patents which are of interest are U.S. Pat. No. 3,374,328 issued Mar. 19, 1968 to F. L. Cameron and entitled "Cartridge Type Fuse With Explosion Pots" and U.S. Pat. No. 3,810,062, issued May 7, 1974 to F. J. Kozacka and entitled, "High Voltage Fuse Having Full Range Clearing Ability". In the above-mentioned patents or applications, the apparatus described therein forms fulgurites, i.e., fused pulverulent arc-quenching material, after a fusing operation has taken place. The fulgurite provides a disadvantage of providing a path for a restrike of the arc current. It would be advantageous if a current limiting fuse could be found or developed which utilized the properties of energy-absorbing, pulverulent, arc-quenching material and localized gas-evolving suppressors, but which additionally reduced the tendency of arc restrike by reducing the tendency of fulgurite formations as a by-product of the fusing operation. It would also be advantageous to provide a wound fuse element which generally remained spaced, one turn from another, before and as long as possible during the fusing operation, to prevent or reduce inter-turn voltage breakdown.